The proposed research encompasses two areas: The first involves the scute locus of Drosophila melanogaster. Recombination in and near this locus will be studied in an effort to obtain data bearing on the Wallace-Kass model of gene control. In many respects this study represents a resurrection (with modern interpretations) of studies carried out by the geneticists of the early 1930's, studies that led Dubinin to the now-discarded subgene hypothesis. The second area can best be referred to as innovative evolution. Mutant strains of D. pseudoobscura and D. persimilis will be used to force the creation of wildtype introgressive laboratory populations. These will be used in the study of sexual isolation; specifically, in estimating the extent of the repertoire of isolating behaviors available to the introgressive populations. The technique of using mutant strains of closely related Drosophila species to force introgressive hybridization promises to be a general technique analogous to the use of mutant strains of Neurospora and minimal medium to force heterokaryosis in this mold. Other studies on innovative evolution will involve the selection of populations of D. melanogaster to toxic substances (or other abnormal circumstances) with the view that the selected populations, when forced to coexist in a single laboratory cage, might develop sexual isolation, thus coexisting as two isolated populations. Diagnostic electrophoretic allozymes will be used where necessary to label the selected populations.